1. Field of the Invention
Embodiments of the present invention generally relate to preheating gases for a semiconductor fabrication process. More specifically, to preheating gases used in deposition and etch reactions on a semiconductor substrate, such as an epitaxial deposition process or other chemical vapor deposition process.
2. Description of the Related Art
Epitaxial growth of silicon and/or germanium-containing films has become increasingly important due to new applications for advanced logic and DRAM devices, among other devices. A key requirement for these applications is a lower temperature process so that device features will not be damaged during fabrication. The lower temperature process is also important for future markets where the feature sizes are in the range of 45 nm to 65 nm, and avoidance of the diffusion of adjacent materials becomes critical. Lower process temperatures may also be required for both substrate cleaning prior to growth of the silicon and/or germanium-containing epitaxial film and during selective or blanket growth of the epitaxial film. By selective growth, it is generally meant that the film grows on a substrate which includes more than one material on the substrate surface, wherein the film selectively grows on a surface of a first material of said substrate, with minimal to no growth on a surface of a second material of said substrate.
Selective and blanket (non-selectively grown) epitaxial films containing silicon and/or germanium, and strained embodiments of such epitaxial films, which are grown at temperatures of less than about 700° C., are required for many current semiconductor applications. Further, it may be desirable to have the removal of native oxide and hydrocarbons prior to formation of the epitaxial film accomplished at temperatures in the range of about 650° C. or less, although higher temperatures may be tolerated when the removal time period is shortened.
This lower temperature processing is not only important to forming a properly functioning device, but it minimizes or prevents the relaxation of metastable strain layers, helps to prevent or minimize dopant diffusion, and helps to prevent segregation of dopant within the epitaxial film structure. Suppression of facet formation and short channel effects, which is enabled by low temperature processing (low thermal budget processing), is a significant factor for obtaining high performance devices.
Current techniques for selective and blanket epitaxial growth of doped and undoped silicon (Si), germanium (Ge), SiGe, and carbon containing films, are typically carried out using reduced pressure chemical vapor deposition (CVD), which is also referred to as RPCVD or low pressure CVD (LPCVD). The typical reduced pressure process, such as below about 200 Torr, is carried out at temperatures above about 700° C., typically above 750° C., to get an acceptable film growth rate. Generally, the precursor compounds for film deposition are silicon and/or germanium containing compounds, such as silanes, germanes, combinations thereof or derivatives thereof. Generally, for selective deposition processes, these precursor compounds are combined with additional reagents, such as chlorine (Cl2), hydrogen chloride (HCl), and optionally hydrogen bromide (HBr), by way of example. A carbon-containing silane precursor compound, for example methylsilane (CH3SiH3), may be used as a dopant. In the alternative, inorganic compounds, such as diborane (B2H6), arsine (AsH3), and phosphine (PH3), by way of example, may also be used as dopants.
In a typical LPCVD process to deposit an epitaxial layer on a substrate, precursors are injected into a processing region in a chamber by a gas distribution assembly, and the precursors are energized above the surface of a substrate in the chamber by irradiation of the precursors in the processing region, which is typically low wavelength radiation, such as in the ultraviolet and/or infrared spectrum. Plasma generation may also be used to dissociate the reactants. The substrate temperature is typically elevated to assist in adsorption of reactive species and/or desorption of process byproducts, and it is desirable to minimize the delta between the precursor temperature in the processing region and the substrate temperature in order to optimize the energization of the precursors and enhance the deposition or desorption process.
To enable a more efficient dissociation process, it is desirable to preheat the precursors prior to delivery to the processing region to enable faster and more efficient dissociation of the precursors above the substrate. Various methods to heat the precursors have been employed, but challenges remain in stabilizing the preheat temperature prior to energization above the substrate surface. For example, the precursor temperature may be elevated to a desired temperature at or before introduction to the gas distribution assembly, but the precursor temperature may be lowered by thermal losses in flowing through the gas distribution assembly and/or along the flow path to the processing region above the substrate.
Therefore, there is a need in the art for an apparatus and method to minimize the temperature range delta between the introduction temperature of precursors and the processing region, and an apparatus and method of preheating precursors at the gas introduction point that also minimizes heat loss prior to dissociation of the precursor.